<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .s1 {
            width: 200px;
            height: 200px;
            background-color: aquamarine;
            float: left;
        }

        .s2 {
            width: 200px;
            height: 200px;
            background-color: firebrick;
            overflow: hidden;
        }
        .inner{

        }
        /* 处理高度塌陷 */
    </style>
</head>
<body>
    <!-- 1、不被浮动元素覆盖
        2.子元素 父元素外边距不会重叠
        3.BFC可以包含浮动的子元素
    
    开启bfc常用：overflow:hidden-->

    <div class="s1">
        <div class="inner"></div>
    </div>
    <div class="s2"></div>
</body>

</html>